This thing's been loads of fun. We built this to hurl anything from paintballs to smaller snowballs, but it can be scaled easily with a few tweaks. As of presentation time we were throwing paintballs 100 meters at about 30 meters/second with a 10 kilogram counterweight. The hook should hold around 40 kilograms, giving us a bit more punch. Might have to try the snowballs this weekend

That's excellent. My daughter and I built a rubberband powered catapault for school a while ago. Wish i had pix, it was a beast. They never specified a limit to the number of rubber bands or power of the device. With a little twisting of about 50 wide rubber bands, the limit became the 3/8" allthread pivot and the 1" dowel for the arm. We built the base out of 2x4's and set it up so she could stand on the ends to anchor it while arming it. initial tests with golf balls yielded similar results to yours. *and some odd looks from the neighbors. We reduced the power considerably before taking it to school.